class_docstr: This class is responsible for building components for semantic segmentation. 
code: def _build_loss(self, loss_name, loss_cfg: dict):
      def _check_helper(loss_cfg, ignore_index):
          if "ignore_index" not in loss_cfg:
              loss_cfg["ignore_index"] = ignore_index
              logger.warning(
                  "Add the `ignore_index` in train_dataset "
                  "class to {} config. We suggest you manually set "
                  "`ignore_index` in {} config.".format(
                      loss_name, loss_name
                  )
              )
          else:
              assert loss_cfg["ignore_index"] == ignore_index, (
                  "the ignore_index in loss and train_dataset must be the same. Currently, loss ignore_index = {}, "
                  "train_dataset ignore_index = {}".format(
                      loss_cfg["ignore_index"], ignore_index
                  )
              )
  
      # check and synchronize the ignore_index in model config and dataset class
      if self.config.train_dataset_cfg["type"] != "Dataset":
          assert hasattr(
              self.train_dataset_class, "IGNORE_INDEX"
          ), "If train_dataset class is not `Dataset`, it must have `IGNORE_INDEX` attr."
          ignore_index = getattr(
              self.train_dataset_class, "IGNORE_INDEX"
          )
          for loss_cfg_i in loss_cfg["types"]:
              if loss_cfg_i["type"] == "MixedLoss":
                  for loss_cfg_j in loss_cfg_i["losses"]:
                      _check_helper(loss_cfg_j, ignore_index)
              else:
                  _check_helper(loss_cfg_i, ignore_index)
  
      self.show_msg(loss_name, loss_cfg)
      loss_dict = {"coef": loss_cfg["coef"], "types": []}
      for item in loss_cfg["types"]:
          loss_dict["types"].append(self.build_component(item))
      return loss_dict
  
imports: import copy
  from typing import Any, Optional
  import yaml
  import paddle
  from paddleseg.utils import logger
  from paddleseg.cvlibs import Builder
  from paddleseg.utils.utils import CachedProperty
  from cvlibs import Config
  from batch_transforms import BoxMaskGenerator
  from .None import manager
  from utils import utils
label_desc: Use image node_id 8 for calling the CPSBuilder obj's underlying member method code with example usage: obj._build_loss(loss_name, loss_cfg) and returns: loss_dict